# GIER: A Danish computer from 1961 with a role in the modern revolution of astronomy

## TL;DR

This paper details the historical significance of the Danish GIER computer from 1961, which contributed to the development of photon counting astrometry, leading to revolutionary space-based measurements like Hipparcos and Gaia.

## Contribution

It highlights the role of the GIER computer in pioneering photon counting astrometry and its influence on modern astronomical satellite missions.

## Key findings

- GIER computer enabled the first implementation of photon counting astrometry.
- The method led to the success of the Hipparcos satellite in revolutionizing astrometry.
- Results from Hipparcos and Gaia have significantly advanced understanding of the cosmos.

## Abstract

A Danish computer, GIER, from 1961 played a vital role in the development of a new method for astrometric measurement. This method, photon counting astrometry, ultimately led to two satellites with a significant role in the modern revolution of astronomy. A GIER was installed at the Hamburg Observatory in 1964 where it was used to implement the entirely new method for the measurement of stellar positions by means of a meridian circle, then the fundamental instrument of astrometry. An expedition to Perth in Western Australia with the instrument and the computer was a success. This method was also implemented in space in the first ever astrometric satellite Hipparcos launched by ESA in 1989. The Hipparcos results published in 1997 revolutionized astrometry with an impact in all branches of astronomy from the solar system and stellar structure to cosmic distances and the dynamics of the Milky Way. In turn, the results paved the way for a successor, the one million times more powerful Gaia astrometry satellite launched by ESA in 2013. Preparations for a Gaia successor in twenty years are making progress.

---
Source: https://tomesphere.com/paper/1704.05828